Iron-based particles have long been used as a base material in the manufacture of structural components by powder metallurgical methods. The iron-based particles are first molded in a die under high pressures to produce a desired shape. After the molding step, the compacted or “green” component usually undergoes a sintering step to impart the necessary strength to the component.
The mechanical properties of compacted and sintered components can be greatly increased by the addition of certain metallurgical additives, such as for example, alloying elements. Alloy steels, for example, are traditionally prepared by mechanically mixing powder alloy additions in elemental form or as oxides. Although convenient due to its simplicity, a disadvantage of this technique is that the resulting alloyed compositions have a heterogeneous structure determined by the thermodynamic and diffusion characteristics of each elemental component. In addition, there have traditionally been problems in preparing homogeneous admixtures where particles of alloying materials are uniformly distributed and would not segregate during transport and handling.
The cost associated with utilizing commonly used metallurgical additives is another disadvantage because it can unfortunately add up to a significant portion of the overall cost of the powder composition. Accordingly, it has always been of interest in the powder metallurgical industry to try to develop less costly metallurgical additives to reduce and/or replace entirely the commonly used alloying elements, such as for example copper or nickel.
Another disadvantage of using metallurgical alloying additives is that they may also impart undesired properties to metallurgical composition. For example, manufacturers of powder metallurgy parts generally desire to limit the amount of copper and/or nickel used in compacted metallurgical parts due to the environmental and/or recycling regulations that control the use or disposal of those parts. Moreover, addition of nickel based metallurgical additives commonly results in the undesirable shrinkage of compacted parts when sintered at high temperatures. The powder metallurgical industry seeks to minimize shrinkage to ensure the dimensions of sintered parts are as close as possible to the dimensions of the compaction die.
Accordingly, there exists a current and long felt need in the powder metallurgical industry to develop alternatives to the use of, or decrease the amount of, various common metallurgical additives in metallurgical powder compositions.